HU220748B1 - Inproved process for producing n,n-dimethyl-cyclohexyl-amine - Google Patents

Abstract

N,N'-di:methyl-cyclohexyl-amine is prepared by an improved method employing reductive amination of cyclohexanone with dimethylamine, at 60-250 degreesC, 15-200 bar pressure in the presence of a liquid catalyst charge of 0.25-0.65 kg/dm3/hr. A 100-600 dm3/dm3 gas/liquid ratio is maintained, as the reaction proceeds in presence of hydrogen gas or in the presence of a hydrogen-gas mixture containing at least 50 volume% hydrogen. The reaction is continuous and the reducing amination is carried out in the presence of at least 1 wt.% trimethylamine calculated on weight of cyclohexanone.

Description

The present invention relates to an improved process for the preparation of N, N-dimethylcyclohexylamine by reacting cyclohexanone with dimethylamine in the presence of hydrogen and a hydrogenation catalyst. The reaction is reductive amination.

Ν, Ν-Dimethylcyclohexylamine is a widely used material. It can be used in the plastics industry as a polymerization catalyst, as an additive to improve fuel storage stability, and as a corrosion inhibitor.

Cyclohexanone is one of the esocyclic ketones which is more difficult to undergo reductive amination reaction than open chain or exocyclic ketones. This is due to the less polar nature of the carbonyl group and the greater steric inhibition. Thus, stricter reaction conditions are required to achieve proper conversion. This is a problem not only because of the increased formation of by-products but also because of the lower yields. Cyclohexanol and monomethylcyclohexylamine are formed as by-products.

Cyclohexanone, as the most practical esocyclic ketone, has been the subject of several publications discussing its reductive N-alkylation. The methods mainly describe reactions with primary amines. The reaction of dimethylamine with cyclohexanone is less discussed.

The Doc. Lags. Nauk. SSSR 226, 1341 (1976), cyclohexanone is aminated in the presence of an alumina supported copper catalyst doped with alkali metal oxides. The maximum yield for N-ethylcyclohexylamine is 59.1%. Lower yields can be obtained with nickel-containing catalysts.

DE 16118155 discloses a process for the preparation of N-methylcyclohexylamine by reductive alkylation of cyclohexanone with methylamine. The reaction is carried out in a hydrogen stream at 100-140 ° C and 50-150 bar in the presence of a chromium-activated cobalt catalyst. Methylamine is used in a very large 18-22-fold excess, yet the target product is obtained in a moderate yield.

The Sb. Vys. See Chem-Technol. Praze, Org. Chem. Technol. C19, 35 (1973) and Czechoslovakian Patent Specification CS 154133, reductive amination of cyclohexanone with methyl and ethylamine on charcoal in the presence of 3% palladium on catalyst; N-monoalkylcyclohexylamines are obtained in a yield of about 80%.

The use of platinum, radium, palladium, ruthenium and molybdenum sulfide catalysts for the reductive amination of cyclohexanone is described in European Patent EP 14985. By this procedure, 84% of the maximum yield was achieved.

The disclosed processes have shown the preparation of N-monoalkylcyclohexylamines. The yields reported are very low.

The following procedures describe the preparation of Ν, Ν-dimethylcyclohexylamine. Their common disadvantage is either the batch mode and / or the presence of a catalyst that is difficult to handle. Excipients are acids or halides, which are potential environmental contaminants.

According to Chinese Patent No. CH 1092061, a palladium on activated carbon catalyst is used in a batch mode.

U.S. Pat. No. 4,521,624 discloses a conversion of 98.78% relative to cyclohexanone on a palladium on activated carbon catalyst in a batch mode. The desired Ν, imet-dimethylcyclohexylamine was obtained in 97.5% yield. A major disadvantage is that the process can only be performed in batch mode.

A good yield (98%) is provided by the continuous operation process disclosed in Hungarian patent application HU 202 190. Here, however, the difficult catalyst treatment is a difficulty, which means promoting the γ-alumina support used with halogen or removing it during activation. This also results in the production of aqueous waste containing halogen.

In batch mode and acetic acid, the process described in U.S. Patent No. 4,954,654 is employed. The catalyst used is the extremely flammable Raney cobalt. Conversion values achieved range from 84.3% to 96.1%, with an average yield of 82% after distillation. The disadvantages of the process are not only the low average yield but also the batch mode, acetic acid and catalyst treatment.

As stated above, owing to their less polarized carbonyl group and steric inhibition of the ring structure, esocyclic ketones are difficult to subject to a reductive amination reaction. Therefore, there is the possibility of side effects. The most likely of the side reactions is the reduction of the keto group, which in the case of cyclohexanone results in a significant formation of cyclohexanol. Due to the relative slowness of the amination reaction, the disproportionation of dimethylamine may also occur, resulting in the conversion of monomethylamine to the undesirable N-methylcyclohexylamine. It is also necessary to suppress these side effects.

It is an object of the present invention to provide a process by which Ν, Ν-dimethylcyclohexylamine can be produced in good yield, suppressing side reactions, in a state-of-the-art continuous mode, without the formation of polluting wastes.

In our experiments it has been found that cyclohexanone can be reductively aminated with dimethylamine in good yield in the presence of hydrogen and a hydrogenation catalyst when at least 1% by weight of trimethylamine is added to the reactants. It has also been found that when the amination is carried out in the presence of trimethylamine, the relative reaction rate between the main reaction and the unwanted side reactions increases significantly in favor of the former. In the absence of trimethylamine, this beneficial effect is not observed.

The present invention therefore relates to an improved process for the preparation of Ν, Ν-dimethylcyclohexylamine by reductive amination of cyclohexanone with dimethylamine in the presence of hydrogen and a hydrogenation catalyst at 60-250 ° C, 15-200 bar, 0.25-0.65 kg / dm ³ catalyst.hours with liquid load maintaining 100-600 dm ³ / dm ³ gas / liquid ratio, calculated for cyclohexanone

EN 220 748 B1 using at least 1% by weight of trimethylamine mixed with the reactants in a continuous mode.

There is no critical upper limit for the amount of trimethylamine to be added to the reactants. However, in practice, more than 20% by weight of trimethylamine relative to cyclohexanone is inappropriate because circulating more inert material is already detrimental to economy.

The hydrogen source may be a gas containing at least 50% by volume of hydrogen. Suitable hydrogenation catalysts are platinum group metals and nickel in particulate form, supported on a support. The carrier may be a modification of alumina, silica, aluminosilicate, carbon, zeolite, alkaline earth metal carbonate. The dimethylamine may be used neat, in solution or in some form in liquid form, which will release the reactive dimethylamine under the reaction conditions. This is the case, for example, with the fantasy name "DIMCARB", marketed by UCB, which is a 1.8 molar liquid complex of dimethylamine and carbon dioxide.

Trimethylamine not only increases the selectivity of the amination but also its productivity, i.e. the amount of amine that can be produced per unit time. According to the state of the art, higher productivity could only be achieved by extensive development. In our experience, the capacity of a given production unit can be increased by 40-60% using our new process.

The reaction may also be carried out continuously in a catalyst charge. However, it has been found that productivity and selectivity can be further increased by passing the reactants through two or more sequentially charged catalyst charges. In this embodiment, the temperature is controlled to increase the average temperature of the successive catalyst beds by 10-30 ° C. It is desirable that the charge quantities be approximately the same.

The rate of the amination reaction can be further increased if excess dimethylamine is used. In our experience, the molar excess is preferably 1.2 to 3 mol dimethylamine / mol cyclohexanone.

The process of the present invention provides N, N-dimethylcyclohexylamine in high yield and excellent selectivity. The target product is isolated by distillation from the other components of the product mixture in a manner known per se. The N, N-dimethylcyclohexylamine thus isolated is very pure and does not require further purification.

The main advantages of the process according to the invention are as follows.

- The process can be performed in a continuous, automated, high-productivity machine.

Due to the presence of trimethylamine and the specially directed reaction, the target product is obtained in high yield and selectivity.

- Different metals can be used as catalysts.

- The procedure does not require the use of specially trained, custom-made equipment.

The invention is illustrated in detail by the following non-limiting Examples.

Example 1

100 cm ^{3 of} 1% Pt / Al ₂ O ₃ catalyst were charged into a pressure-tight tube reactor. Ammonia synthesis gas (75 volumes of hydrogen to 25 volumes of nitrogen) was set at a pressure of 60 bar and a gas flow rate of 16 dm ³ / h. Then, the reactor was operated at 140 ° C with a liquid load of 0.4 g / cm ³ catalyst. The composition of the feedstock by weight was as follows: cyclohexanone 43.5 dimethylamine 30, water 20, trimethylamine 6.5. The cyclohexanone fed was completely transformed, yielding the desired N, N-dimethylcyclohexylamine in 98.2% yield.

Example 2

3 x 100 cm ^{3 of} 1% Pt / Al ₂ O ₃ catalyst were charged into pressure-tight tube reactors. Ammonia synthesis gas (75% by volume hydrogen to 25% by volume nitrogen) was adjusted to a pressure of 60 bar and a gas flow rate of 45 dm ³ / h. Then, 0.6 g / cm ^{3 of} catalyst / hour catalyst fluid reactors were operated at 120/140/155 ° C. The composition of the feedstock by weight was as follows: cyclohexanone 38.7, dimethylamine 32.2, water 22.3, trimethylamine 6.8. The supplied cyclohexanone was completely transformed to give the desired N, N-dimethylcyclohexylamine in 99.3% yield.

Example 3

3 x 100 cm ³ 50% Ni / Al ₂ O ₃ catalyst was charged into pressure-tight tube reactors. The catalyst was reduced in a manner known per se. Hydrogen was used to set a pressure of 130 bar and a gas flow rate of 30 dm ³ / h. Then, 0.48 g / cm ^{3 of} catalyst / hour catalyst fluid reactors were operated at 140/165/180 ° C. The composition of the feedstock by weight was as follows: cyclohexanone 48.1, dimethylamine 43.3, water 0, trimethylamine 8.6. The cyclohexanone fed was 99% converted to the desired N, N-dimethylcyclohexylamine in 97.8% yield.

Example 4

100 cm ^{3 of} 0.5% Pd / Al ₂ O ₃ catalyst was charged to pressure-tube reactors. Ammonia synthesis gas (75% by volume hydrogen to 25% by volume nitrogen) was set at a pressure of 45 bar and a gas flow rate of 18 dm ³ / h. Then, the reactor was operated at 145 ° C under a liquid load of 0.36 g / cm ³ catalyst. The composition of the feedstock by weight was as follows: cyclohexanone 43.5, dimethylamine 30, water 20, trimethylamine 6.5. The cyclohexanone fed was completely transformed, yielding the desired N, N-dimethylcyclohexylamine in 98.7% yield.

Example 5

100 cm ^{3 of} 0.5% Pd / Al ₂ O ₃ catalyst was charged to pressure-tube reactors. Ammonia synthesis gas (75% by volume hydrogen to 25% by volume nitrogen) was adjusted to a pressure of 50 bar and a gas flow rate of 18 dm ³ / h. The reactor was then operated at 155 ° C under a liquid load of 0.33 g / cm ³ catalyst.

HU 220 748 Bl

The composition of the feedstock was as follows: cyclohexanone 40, dimethylamine 31, carbon dioxide 16.8, trimethylamine 4.2, water 7.9. The cyclohexanone fed was completely transformed to give the desired N, N-dimethylcyclohexylamine in 98% yield.

Example 6

This example is provided for comparison purposes.

100 cm ^{3 of} 1% Pt / Al ₂ O ₃ catalyst were charged into pressure-tube reactors. Ammonia synthesis gas (75% by volume hydrogen to 25% by volume nitrogen) was adjusted to a pressure of 60 bar and a gas flow rate of 16 dm ³ / h. Then, the reactor was operated at 140 ° C with a liquid load of 0.4 g / cm ³ catalyst. The weight ratio of the feedstock was: cyclohexanone 46.5, dimethylamine 32.1, water 21.4, trimethylamine 0. The cyclohexanone fed was 97.3% converted to the desired N, N-. dimethylcyclohexylamine was formed in 81.4% yield.

Claims (5)

PATENT CLAIMS A process for the preparation of Ν, Ν-dimethylcyclohexylamine by reductive amination of cyclohexanone with dimethylamine at 60-250 ° C, 15-200 bar, 0.25-0.65 kg / dm ^{3 of} catalyst per hour of liquid loading, 100 Maintaining a gas / liquid ratio of -600 dm ³ / dm ^{3 in the} presence of a catalyst and a gas mixture containing hydrogen or at least 50% by volume hydrogen, characterized in that reductive amination is carried out in the presence of at least 1% by weight of trimethylamine per cyclohexanone. Process according to claim 1, characterized in that the reductive amination is carried out in the presence of up to 20% by weight of trimethylamine relative to cyclohexanone. 3. The process according to claim 1 or 2, wherein the dimethylamine is used in pure form, in solution or in the form of a liquid providing a reactive dimethylamine under the reaction conditions. 4. Process according to any one of claims 1 to 3, characterized in that the dimethylamine is used in a molar excess of 1.2-3 with respect to cyclohexanone. 5. A process according to any one of claims 1 to 5, wherein the reaction is conducted in a continuous mode on two or more catalyst beds so that the average temperature of the successive catalyst beds is increased by 10-30 ° C.